Sealed electrical switches



March 12, 1957 R. J. CASSIDY SEALED ELECTRICAL SWITCHES Filed June 16, 1953 1N VEN TOR. #05597- J (Ass/0y United States Patent SEALED ELECTRICAL SWITCHES Robert J. Cassidy, Mansfield, Ohio Application June 16, 1953, Serial No. 363,773

(Filed under Rule 470)) and 35 U. S. C. 118) Claims. (Cl. 200-438) This invention relates to electrical switches and, more particularly, to a construction and procedure by which the terminals of, and lead wires connected to, electrical switches may be sealed against the passage of air, moisture, gases, vapors or the like.

It is customary to provide electrical switches with housings or enclosures of various types. However, when an enclosed switch that is not completely sealed is exposed to different external atmospheric or gaseous pressures, or to changes of temperature, the device breathes. That is, there is a transfer of air or other gas and/or vapors from the exterior to the interior of the switch housing and, when this is accompanied by a tempera ture change, vapors thus entering the housing are condensed and accumulate therein. For example, it has been found that enclosed switches employed in aircraft frequently accumulate considerable quantities of Water. This results in corrosion and other difiiculties. Similar difficulties are encountered with switches in other environments such as in refrigerated chambers or the like.

his, therefore, imperative that enclosed switches be sealed against transfer of air, moisture, vapors, or the like, between the exterior and the interior of the switches. However, it has, heretofore, been expensive and dimcult to effectively seal such switches and the scaling is especially difiicult in the region of the switch terminals and of the conductors or leads connected thereto. This is due, at least in part, to the different coefiicients of thermal expansion of the materials customarily employed for these parts and to lack of complete sealing between the lead wires and the insulation therefor thereby permitting passage of gases therebetween. The latter condition is accentuated when the lead wires are stranded since vapors, moisture and the like can travel to the switch between the strands of the wire.

An object of this invention is to provide an improved method of sealing electrical switches against passage of moisture, vapor, or other gases about the terminals thereof and the conductive members attached thereto, which method is inexpensive, is easily and rapidly performed and results in a rugged construction that is not damaged by shock, vibration, normally encountered temperature changes, or other operating conditions.

Another object of the invention is to provide an improved electrical switch construction and method of producing the same wherein the switch terminal members, and the portions of the conductive members connected thereto, are sealed against passage of gas, vapor or the like, by a foamed-in-place palstic.

A further object of the invention is to provide an improved electrical switch construction and method of producing the same wherein the ends of the conductive members connected to the switch terminals, whether these be single strand or multiple strand wires, are sealed so that air, gas or other vapors cannot enter the switch through spaces between the insulation and the Wires or between the strands of the latter when the wires are of the multiple strand type.

ice

A more specific object of the invention is to provide an improved electrical switch construction and method of producing the same wherein the moving parts of the switch are enclosed in an impervious housing with the terminal members projecting therefrom through openings therein, which openings, together with the terminal members and the portions of the conductive members connected thereto, are sealed against passage of gas, vapor, or the like, by the reaction product of a mixture comprising an isocyanate and a resinous polymer.

The invention further resides in certain novel features of switch construction and in the method of producing the same, and further objects and advantages of the invention will be apparent to those skilled in the art to which the invention pertains from the following description of certain embodiments thereof which are described with reference to the accompanying drawing, forming a part of this application, and in which:

Fig. 1 is an enlarged vertical sectional view through the presently preferred embodiment of a switch constructed in accordance with this invention, the view being taken substantially on the irregular line 11 of Fig. 2;

Fig. 2 is a transverse sectional view through the switch shown in Fig. l, the view being taken substantially along the line 2-2 of Fig. 1;

Fig. 3 is an enlarged vertical sectional view through a modified embodiment of the invention; and

Fig. 4 is a view, partially in transverse section and partially in top elevation, of the switch shown in Fig. 3, the view being taken substantially on the line 44 of Fig. 3.

The switch shown in Figs. 1 and 2 comprises a base or supporting member 16 which is preferably formed of metal and has a terminal post or stud 11 secured thereto. As here shown, the post or stud 11 has a reduced diameter shank 12 passing through an opening of larger diameter in the base, the outer end of which shank is upset to secure the post to a terminal member or bracket 13 in a well-known manner. Insulating material, such as sheets 14 and 15 of mica or the like, is provided between the larger diameter portion of the stud or post and the base It and between the base 10 and the terminal member or bracket 13. The lower end of the terminal post or stud 11 has one end of an over-center or buckling spring 16 secured thereto which spring comprises a central portion that is bowed or dished with respect to the peripheral and end portions of the member. The curvature of this central portion is adapted to be reversed upon application of a force thereto and this reversal of curvature moves the free end of the spring member with a snap action.

The free end of the spring 16 is provided with a contact 17 which is the moving contact of the switch and is adapted to move to and from engagement with a stationary contact 18. The contact 18 comprises a substantially horizontally extending member one end of which is secured to the base 16 by a terminal post or stud 19, similar to the post or stud 11, the upper end of which is connected to a terminal member or bracket 20. Movement of the contact 17 to its other position, that is, out of engagement with respect to the contact 18 is limited by an adjustable stud or screw 21 which is threaded in one end of a horizontally extending member 22, the other end of which is secured to the base 10 by means of a post or stud 23 similar to the posts or studs 12 and 19. The screw 21 may provide a second stationary contact for the switch if this be desired and hence the upper end of the post or stud 23 is likewise provided with a terminal member or bracket.

The lower end of the post 11 is also provided with a resilient arm or member 24 that is secured to the post or stud 11 above the over-center spring 16 with the forward tion. of the spring member..16.. .Thisend of the arm 24 is provided with a projection 25, such as a ceramic button or the like, which is adapted to contact the surface The arm 24 is side thereof opposite the arm 24.

In. the. embodiment of theswitch illustrated in l and 2, the force for operating the movable contact a thermal responsive member, here shown as a three-armed bimetallic member 26 .having a shape similar to that .which is formed by removing arcuate sectors from a con- 1veXo-"concave disc-like member.

The aims of the bime- -.:tallic memben26 are supported adjacent their ends upon araised prti'on27i of a :housing or shell member'23.

This housing or shell-member has a closed bottom and rhas the sidewall thereof substantiallycylindrical in cenfiguration. and provided with a radially outwardly extending flange 29 adjacent its upper edge. The flange portion .29'of the shell is secured to the base it}, as for example,

. by welding orsoldering, thereby providing an enclosure for the switch with the terminal members projecting thereabove.

i The central portion of the bimetallic member'26 is provided with a boss 30 which is tapped to receive an adjustable force transmitting member 3i. As here shown,

1. the member 31 is in the form of a screw, the inner end of which is provided with an insert or projection 32 formed of ceramic or other insulating material. Theouter end of the insert 32 is preferably curved'and engages 1.the-lower surface of the spring member 16 substantially centrally of the bowed or curved portion thereof.

The construction described is such that, when the bimetallic member 26 is subjected to a predetermined temperature, it flexes so that the force transmitting member 31 acts through the member or projection 32 to apply :force to the spring 16. This reverses the curvature of the u spring, the arm 24 yielding sufficiently to allow such reversal. The reversed curvature of the spring 16 moves .the contact 17 from engagement with the contact 18, the

extent of movement being limited by the abutment or screw 21. When the temperature of the bimetallic member 26 is again reduced, the member returns to its initial position whereupon the spring arm 24 restoresthe overcenter'spring 16 t0 the position as shown in Fig. 1, thus returning the movable contact 17 into engagement with the stationary contact 18. The contacts 17 and 18 may be made to control an electrical circuit by providing suitable conductive members or lead wires 33 and 34 which are connected, respectively, to the terminal members or brackets 13 and 2h. As mentioned above, the switch may also be employed as a three contact switch, if desired, in which event the third conductor or lead 'wire 35 is connected to the terminal member or bracket provided on stud 23.

Adjustment of the switch operation is effected by adjusting the position of the member 31 relative to the bimetal member 26.. This may be effected prior to assembly of the shell or housing with the base It) in which event the lower end of the housing or shell may be completely closed. Preferably, however, a central opening I is left in the closed end of the shell or housing 28 which opening provides access to the end of the member 31 so that adjustmentthereof can be effected after the switch is completely assembled. This opening may then be closed by a disc-like plug 36 which is secured to the housing or shell by soldering, brazing or the like. The adjustable screw or stud 21 provides a means for adjusting the 'amount of contact separation as will be readily apparent to those skilled inthe art.

'Although the switch as thus far described has the operating-parts enclosed, the switch would be subject to breathing or transfer of air, vapor or gases between the ...interior and exterior thereof. as theresult of changes of temperature and/ or pressure of the environment in which the switch is placed. This is due to the fact that it is substantially impossible to seal the openings for the terminal members through the base simply by maintaining close manufacturing tolerances, firmly riveting, 'or other conventional expedients. Moreover, conventional compounds such as sealingwax, thermoplastic resins, and the like do not provide an elfective seal since they tend to shrink from the parts upon changes of temperature and/ or moisture content and some of these substances, in addition, tend to take up moisture which is highly undesirable. Ithas therefore been conventional practice heretofore to eifectsealing of the terminal members and/or conductive leads by means of glass, rubber or the like. While the use of glass about the terminal members and leads does provide an effective seal, this is fragile as well as being relatively difiicult to achieve in mass production at low cost] The conventional rubber sealingmeans, in general, do not completely seal'unle'ss the rubber be vulcanized or molded aboutthe parts which likewise is an expensive and time consuming operation.

In accordance with this invention, the switch construction is effectively sealed against breathing and/or other transfer of gas, air, or vapors about the terminal members and .the conductive means or leads connected thereto. Moreover, theterminal members and conductive means are so sealed that no corrosion can occur at this point nor can there. be gas or vapor leakage-between the insulation for the conductive means or leads and the conductive portions thereof or between the strands where stranded wire is used. This sealing is effected by embedding the terminal members and lead wires in a substance of the type known as a foamed-in-place plastic. Such .materialhas the characteristic of expanding during the reaction or setting thereof and firmly adheres to the objects with which it is in contact.

' mixing thereof, will react with the release of carbon dibers or leads 33, 34 and 35.

..oxide which forms a multitude of cells that are substantially not interconnected. The reaction causes expansion of the material to many times the initial volume of the mixed liquids and, after the reaction is complete, the product is a solid of good thermal stability which does not shrink or separate from the surfaces with which it is in in effecting sealing of the switch construction shown in Pig. .1, a rigid enclosure 37 is provided about theterminal -members or brackets and the ends of the conductive memopening in the housing is necessary. A grommet or sleeve 40 of rubber or the like is either molded integrally with theinsulation'39 or may be made separate therefrom and either cemented thereto or have a pressure fit thereon. This grommet has a shank portion fitting in the opening of the enclosure 37 and an enlarged head portion 41 surrounding the opening and engaging the inner surface of the side wall adjacent the opening.

The enclosure member 37 has a second opening 42 preferably in the top thereof through which the mixture of the isocyanate and resinous polymer is introduced which mixture thereafter reacts to provide the aforementioned foamed-in-place plastic that completely fills the space between the enclosure'37 and the base it). During the reaction of the mixture which results in the formation of the solid plastic 43, the opening 42 in the enclosure 37 is temporarily closed by a suitable means not shown and consequently, the expansion of the plastic material exerts a pressure within the enclosure 37 so that all openings about the terminal members and lead wires are completely closed. Moreover, the ends of the conductors or lead wires are embedded and sealed within the plastic material and the head portion 41 of the grommet 4b is tightly compressed against the housing and about the insulation 39 and the wires contained therein. Therefore, the ends of the lead wires and the terminal workers are sealed so that no vapors or gases can reach them or enter the switch through openings thereabout.

The plastic material 43 is rugged and non-fragile and consequently is not broken or separated from the parts with which it is in contact by vibration, shocks, or other mechanical forces to which the switch is normally subjected, nor is the plastic softened or physically changed by normal temperature variations. Moreover, the material is an electrical insulator and is not deteriorated by moisture or fumes such as encountered in aircraft or similar installations. Therefore, sealing of the switch terminals and lead wires by this method not only provides an effective barrier against vapors or gases entering or leaving the switch at this location but is also more durable than the conventional glass seals heretofore employed. Furthermore, this improved method of sealing is readily adapted to mass production techniques and gr atly reduces the cost of manufacture of scaled switches.

The principles of this invention may be applied in sealing switch terminals and leads for switches constructed other than as illustrated in Figs. 1 and 2. For example, Figs. 3 and 4 show an embodiment of the invention wherein the switch elements are supported and enclosed within a substantially cupshaped housing 44 by means of a single vertically extending stud or mounting member 45. The housing member 44 is preferably formed of metal and the stud 45 is provided with a metal member or washer 46 to space a thermal responsive member, such as a bimetallic strip 4-7, from the housing and provide good thermal transfer therebetween. The bimetallic strip 47 is also mounted on the stud 55 with a contact carrying arm 48 supported thereabove. The arm 48 is formed of metal and is resilient, the arm or member 43 being insulated from the bimetallic member 47 by a washer or the like 4?. As shown, the washer 49 has axially extending portions at the top and bottom which portions are of lesser diameter than the main body of the washer and extend into enlarged openings in the thermal responsive member and the arm 48.

The outer end of the contact carrying arm 48 has a substantially U-shaped configuration with a contact surface or projection 50 provided on one of the legs or branches of the U, the contact 5d being adapted to cooperate with a contact 51 provided on the free end of an overcenter spring 52. The over-center spring 52 is of conventional construction and has a central portion of substantially convexo-concave configuration which is adapted to snap through center and reverse its curvature upon application of a force thereto thereby moving the free end of the spring. The end of the spring 52, opposite the contact 5 is mounted upon the stud 45 in conductive relationship therewith and in superposed relationship with the arm 43 but separated therefrom by an insulating washer 53.

Extending above the over-center spring 52 is a relatively rigid arm or member 54, one end of which is supported on the post 45 in spaced relationship with the spring 52 and insulated therefrom by a washer 55. The arm or member 54 has a boss or bushing 56 thereon which is tapped to receive a threaded adjustable abutment member 57. As here shown, the member 57 has the lower portion thereof provided with an insert, such as a pin 58, of ceramic or like insulating material. The lower end of the pin 58 is curved and engages the over-center spring at substantially the central part thereof to limit movement of this portion of the spring. Movement of the outer end of the spring 52 away from the contact St) is limited by an adjustable abutment in the form of a threaded member 59 screwed into a tapped boss or bushing 60 on the second arm or leg of the lJ-shaped portion of the member 48. The lower end of the adjustment member 5'9 is preferably provided with an insulating insert 61 formed of ceramic material or the like, the construction of this adjustable abutment member being similar to the adjustable abutment member 57, 5-3.

In addition to the contact 5%, the arm is provided with an abutment or projection 62 of insulating material extending upwardly from the member and adapted to contact the over-center spring in the region substantially beneath the point of contact of the pin 58 on the adjusting member 57. it will also be noted that the end of the bimetal member or strip 47 is provided with a force transmitting member or projection 63 which is formed of ceramic or other insulating material and is in engagement with the free end of the arm 48 adjacent the outer end of the latter.

The construction described is such that when the bimetallic member or strip 47 has attained a predetermined temperature, it will curve upwardly and this motion is transmitted by the projection 63 to the arm 48 and through the contacts 56 and 51 to the spring 52. When this curvature of the bimetallic member has produced sufiicient movement of the spring 52, the curvature of the central portion of the latter is reversed with a snap action whereupon the central portion thereof engages the projection 62 on the arm 48 while the contact 51 moves from engagement with the contact 56, the extent of the movement of this portion of the spring being limited by the abutment 61. When the temperature falls below the predetermined value, the curvature of the bimetallic member 47 will be reduced sufficiently that it will permit the member 48 to resume the position substantially as shown in Fig. 3, movement of the member 48 being due to the resiliency thereof which normally tends to restore the member to this position. This movement of the arm or member 48 will cause the projection 61 to move the end of the spring 52 while the projection 62 acts upon the center of the latter so that the spring again snaps through center returning to the position substantially as shown in Fig. 3 thereby again engaging the contacts 51 and 5b.

The spring operation may be adjusted by threading the members 57 and/ or 59 relative to the bosses or bushings in which they are mounted and this may be done before the switch is enclosed. Preferably, however, the switch housing 44 is closed by a cover member 63 which rests upon a flange of the housing 44 and is soldered thereto as indicated at 64. This cover member 63 has an opening opposite each of the adjusting members 57 and 59 so that the members are accessible for adjustment after the switch has been enclosed. These adjusting openings may then be sealed by plug or disc members such as 65 and 66 which are secured to the cover member 63 by soldering or the like.

In the embodiment shown in Figs. 3 and 4, the housing 44 of the switch provides one part of an electrical circuit controlled by the switch. Therefore, the switch housing preferably has an arcuate portion of insulating material, such as a sheet 67 of mica or the like, within the housing adjacent the end of the member 47 to provide proper insulation between this member and the housing. As mentioned before, the spring 52 is in electrical conductive relationship with the housing 44 by having the mounting opening for the spring closely fitted about the stud 45. An additional connection may be provided between the spring and housing if this should be found desirable.

The arm 48 of the switch is connected to the other portion of the circuit in which the switch operates. This plastic.

member 68 upon the post 4-5 in engagement with the arm'48 and extending the member 63 adjacent the side wall of the housing 4-4 where the member is connected to a stud 69. The stud d9 extends through an opening in the side wall, and is connected to a terminal member 70 exteriorly of the side wall. The connecting member 68 and terminal 79 are insulated from the sidewall by insulating washers 71 and 72 on either side thereof and by .a washer or sleeve 73 Within the opening in the housing between the washers 71 and 72. The outer end of the terminal member 7 d is adapted to receive a conductor or lead wire 7 i which may be formed of stranded Wire or of single conductor, as may be desired, and is provided with insulation '75.

In order to prevent breathing and/ or other transfer of air, gas, vapors, moisture, or the like into and out of the switch housing about the stud 69, and to prevent corrosion of the lead wire and terminal members as well as to effectively seal these parts, the switch shown in Fig. 3 is provided with a rigid enclosure 76 surrounding the terminal member 79 and the adjacent portion of the conductive member or lead wire. This enclosure 76 is shown as being substantially cylindrical in. configuration with a flange portion 77 at one end received in an annular groove provided in the side wall of the housing 44 concentric with the terminal member 79. The opposite end of the enclosure 76 has an opening for passage of the conductive member or lead 74 and this opening is closed by a rubbergrommet or bushing 78, which is secured to the insul tion 75 by molding it integrally therewith or by vulcanizing or cementing it thereto. Within the housing 76 and surrounding the base of the terminal member 70, so as to overlie the stud 69 and substantially cover. the opening at the flange portion 77, is a sheet or washer 79 of rubber or like resilient material.

.The space betweenthe grommet 78 and the sheet or WQSi'lfiZf 79 is completely filled with a foamed-in-place This is effected byvirtue of the fact that the enclosure 76 has an opening 8t adjacent thetop thereof through which a mixture, comprising an isocyanate and a resinous polymer, is introduced in suficient quantity so that the resultingreaction will cause foaming of the material and resulting expansion thereof so that it completely fills the enclosure 76and exerts pressure upon the grommet 73'and the washer or sheet 79. .Consequently, the terminal member. 70 and. the conductive member 74 will be entirely surrounded or embedded in the resulting cellular solid and the opening about the terminal member and its stud 69 into the switch housing will be completely sealed as will also the end of-the insulation and the conductor 74 extending therethrough.

As will now be apparent from the similar procedure described with respect to Figs. 1' and 2, the opening 80 is normally closed during this reaction by means ofa temporary cover so that the desired .pressuremay develop within the enclosure 76. The opening may be left uncovered after the reaction is complete or it may be permanently closed, if desired, by a plug or disc, 81 fitted thereover. One way in which this may be accomplished is by soldering the disc or plug to the enclosure after the reaction is completed. Alternatively, the plug or disc. 81 may be placed over the opening 80 las soon as ,the mixture is introduced into the enclosure and beforethe reaction begins. This plug or disc 81 may then be clamped or held in place during the reaction whereupon the foamed-in-place material in forming the, cellular solid 82 will contact the disc 31 and adhere thereto so that when the reaction is complete, the force used. in clamping the plug or disc 81- maybe removed and this-member will remain in place, being held'by the plastic material 82.

It will be apparent that the'principles of thisinvention may be applied to scaling the terminals and/or adjacent portions of the conductive members of an 'electricalswitch,

d having a construction other thanthosehere illustrated, and that the sealing may be effected in the samemanner with separate conductive leads or wires entering the housing or enclosure through separate openings so that it is not necessary for all conductors to be enclosed in a common sheath. Moreover, attention is directed to the fact that the sealing material isstable and does not need protection so that the nature of the enclosure such as 37 and 76 may be varied from those shown, the purpose of which are primarily to provide a form in which the sealmaterial may expand and set. It will be evident from these and other adaptations and modifications of the invention which will readily occur to those skilled in this art that the invention should not be limited to the specific details of construction here shown and described but only by the spirit and scope of the appended claims.

Having thus described my invention, 1 claim:

1. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch comprising providing an impervious enclosure for the switch with conductive means connected to the switch extending through an opening therein, surrounding the said conductive means with a flexible material in the region where said means pass through said opening and compressing said flexible material about said conductive means and into sealing relationship with said opening by forming a foamedin-place plastic in contact therewith and which plastic is applied thereto in a confining chamber which is sealed during the setting of the plastic to pressurize said chamber. p

2. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch comprising providing an impervious housing for the switch with the conductive means connected to said switch extending outwardly therefrom, providing a rigid enclosure about the portion of said conductive means externally of said housing in spaced relationship to said conductive means, providing a flexible material about said means in the region thereof where said means extends from said enclosure, and filling said enclosure with a foamed-in-place plastic and sealing said enclosure during the setting or" the plastic to pressurize the interior of the enclosure thereby compressing said flexible material about said conductive means and into sealing relationship with said enclosure.

3. The method as defined in claim 2 wherein the foamed-in-place plastic is provided by introducing into said enclosure a mixture comprising an isocyanate and a resinous polymer in quantities such that the said mixture reacts and expands forming a solid and exerts pressure upon the said flexible material to eifect the said sealing.

4. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch about the terminals thereof comprising providing an impervious housing for the switch with the terminal members of the switch projecting therefrom, providing a hollow enclosure for said terminals and which is provided with a passage for and closely surrounding conductor means connected with the terminals, and forming a foamed-in-place plastic in said enclosure in a manner and in sufiicient quantity to completely fill the latter when sealed and exert pressure therein during the formation so that the projecting terminals and housing and the passage in the enclosure for the conductive means are sealed.

5. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch about the terminals thereof comprising providing an impervious housing for the switch with the terminal members of the switch projecting therefrom, providing a hollow enclosure for said terminals with an opening for conductive means to extend therethrough and connect with the terminals, providing a flexible grommet about the said conductive means and extending through the last-mentioned opening,.and forming a foamed-in-place plastic in said enclosure in a manner and quantities such as to completely fill the latter "when sealed and exert pressure therein and on said grom- 9 met, whereby the said grommet seals the conductive means and the opening to the said enclosure from the passage of air, gas, or vapors.

6. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch about the terminals thereof comprisng providing an impervious housing for the switch with the terminal members of the switch projecting therefrom, providing a hollow enclosure for said terminals with an opening for conductive means to extend therethrough and connect with the terminals, providing a flexible grommet about the said conductive means and extending through the last-mentioned opening, and introducing into said enclosure a mixture comprising an isocyanate and a resinous polymer in a manner and in quantities such that the mixture reacts and expands with the enclosure sealed to form a solid completely filling the enclosure and exerting pressure upon said grommet so that the grommet is compressed about said conductive means and into sealing relationship with the opening to said enclosure.

7. The method as defined in claim 6 and further comprising inserting flexible material in said enclosure adjacent said terminals before the said mixture is introduced therein whereby the flexible material is forced into sealing engagement with said housing about said terminals by the solid formed by said mixture.

8. The method of preventing the passage of air, gas, or vapors into and out of an electrical switch comprising providing an impervious housing for the switch with the conductive means connected to said switch extending externally of the housing, providing a rigid enclosure about the portion of said conductive means externally of said housing, said enclosure having an opening through which a portion of the conductive means connected to said switch may extend, providing a rubber grommet about said conductive means in the region of the latter where it extends from said enclosure, inserting into said enclosure a mixture comprising an isocyanate and a resinous polymer in quantities such that the solid reaction product thereof will completely fill said enclosure, and closing all openings to said enclosure so that the expansion of said mixture in reacting exerts pressure upon said grommet thereby compressing it about said conductive means and into sealing relationship with the opening in said enclosure.

9. An electrical switch comprising a housing, cooperating contact means in said housing, means within said housing for controlling engagement and disengagement of said contact means, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure surrounding said terminal means and a portion of said conductive means in spaced relationship thereto and provided with passage means for and closely surrounding said conductive means, and a solid foamed-in-place plastic completely filling said enclosure and exerting pressure in all directions thereby sealing the said conductive means and passage means and said housing in the region of said terminal means.

10. An electrical switch comprising a housing, cooperating contact means in said housing, means within said housing for controlling engagement and disengagement of said contact means, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure surrounding said terminal means and a portion of said conductive means in spaced relationship thereto and having an opening therein through which the said conductive means extends, a flexible grommet means surrounding the said conductive means and extending through the said opening in said enclosure and filling said opening, and a solid foamedin-place plastic completely filling said enclosure and exerting pressure in all directions thereby sealing said housing in the region of said terminal means and compressing the portion of the grommet means within the enclosure about the conductive means and forcing said grommet 10 means into sealing engagement with the enclosure at said opening by the pressure of the said plastic.

11. An electrical switch as defined in claim 9 wherein the said foamed-in-place plastic is the reaction product of a mixture comprising an isocyanate and a resinous polymer.

12. An electrical switch comprising a housing, cooperating contact means in said housing, thermal responsive means in said housing for controlling engagement and disengagement of said contact means, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure surrounding said terminal means and a portion of said conductive means in spaced relationship thereto and having passage means closely fitting and through which the said conductive means extends, and a solid foamed-in-place plastic completely filling said enclosure and surrounding the said terminal means and the said portion of the conductive means therein and exerting pressure thereon thereby sealing the said housing in the region of the said terminal means and said passage means.

13. An electrical switch comprising a housing, cooperating contact means in said housing, means to move one of said contact means with a snap action relative to the other, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure surrounding said terminal means and the portion of the conductive means connected thereto in spaced relationship therefrom and having passage means closely fitting and through which the conductive means extends, and a solid foamed-in-place plastic completely filling said enclosure and surrounding the said terminal means and the portions of the said conductive means connected thereto and exerting pressure on said terminal means and said portions of said conductive means thereby sealing the said housing and conductive means in the region of the terminal means and said passage means.

14. An electrical switch comprising a housing, cooperating contact means in said housing, means in said housing for controlling engagement and disengagement of said contact means, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure surrounding said terminal means and the portion of the conductive means connected thereto in spaced relationship therefrom and provided with passage means closely fitting and through which the said conductive means extends, and a solid foamed-in-place plastic comprising the solid reaction product of a mixture including an isocyanate and a resinous polymer completely filling the said enclosure and exerting pressure in all directions thereby sealing all openings about the said terminal means and said passage means and conductive means.

15. An electrical switch comprising a housing, cooperating contact means in said housing, means within said housing for controlling engagement and disengagement of said contact means, switch terminal means extending from said housing, conductive means connected to said terminal means, an enclosure connected to said housing and surrounding said terminal means in spaced relationship thereto with an opening in said enclosure through which the said conductive means extend, a rubber grommet surrounding said conductive means with a portion disposed within said enclosure and another portion extending through said opening and filling the latter, and a solid foamed-in-place plastic completely filling said enclosure and exerting pressure therein in all directions thereby deforming said grommet into sealing engagement with the conductive means and enclosure and sealing the opening to said housing for said terminal means.

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